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  • Title: Guanine nucleotides modulate the ligand binding properties of cell surface folate receptors in Dictyostelium discoideum.
    Author: De Wit RJ, Bulgakov R.
    Journal: FEBS Lett; 1985 Jan 07; 179(2):257-61. PubMed ID: 3838158.
    Abstract:
    Dictyostelium discoideum cells show 2 distinct classes of cell surface binding sites for folates. One type is non-specific, i.e., binds folic acid (FA), 2-deaminofolic acid (DAFA), and methotrexate (MTX) with similar affinity (K0.5 congruent to 140 nM). Scatchard analysis of this non-specific binding type suggests either heterogeneity or negative cooperativity. Isolated D. discoideum membranes show similar binding characteristics. Guanine nucleotides changed the binding levels of [3H]MTX. In the presence of 0.1 mM GTP, the number of binding sites remains unchanged, while the affinity decreases. GDP and guanylyl imidodiphosphate (GPPNP) are required at about 20-fold higher concentration than GTP, which elicits a half-maximal effect at 15 microM. Other guanine and adenine nucleotides are ineffective up to 1 mM. These results suggests that the non-specific cell surface receptor for folic acid interacts with a guanine nucleotide regulatory (G-) protein.
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